gztell
Hi, I got an alternative for those zipped strings that gzuncompress() cannot extract.
It is a bit better than previous options as it do not create any temporary files, but it has to encode the string in base64, meaning it won't be as fast as a native equivalent (which is probably going to be gzdecode())
<?php
if (!function_exists('gzdecode')) {
function gzdecode($string) { // no support for 2nd argument
return file_get_contents('compress.zlib://data:who/cares;base64,'. base64_encode($string));
}
}
?>
gzuncompress
(PHP 4 >= 4.0.1, PHP 5)
gzuncompress — Uncompress a compressed string
Description
string gzuncompress
( string
$data
[, int $length = 0
] )This function uncompress a compressed string.
Return Values
The original uncompressed data or FALSE on error.
The function will return an error if the uncompressed data is more than
32768 times the length of the compressed input data
or more than the optional parameter length.
Examples
Example #1 gzuncompress() example
<?php
$compressed = gzcompress('Compress me', 9);
$uncompressed = gzuncompress($compressed);
echo $uncompressed;
?>
See Also
- gzcompress() - Compress a string
- gzinflate() - Inflate a deflated string
- gzdeflate() - Deflate a string
- gzencode() - Create a gzip compressed string
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User Contributed Notes
gzuncompress - [7 notes]
MagicalTux at php dot net ¶
2 years ago
squeegee ¶
3 years ago
One way to uncompress zlib-compressed data that is in a file without first reading in the file and then gzuncompressing it (maybe you have memory problems doing it that way) is to compile the zpipe.c program from zlib ( http://www.zlib.net/zpipe.c )...
on linux, etc:
# gcc -lz -o zpipe zpipe.c
# cp zpipe /usr/local/bin
Then do this
<?php
$uncompressed = shell_exec("cat $compressed_file | zpipe -d");
?>
heavyccasey at gmail dot com ¶
5 years ago
Note that gzuncompress() may not decompress some compressed strings and return a Data Error.
The problem could be that the outside compressed string has a CRC32 checksum at the end of the file instead of Adler-32, like PHP expects.
Workaround:
<?php
function gzuncompress_crc32($data) {
$f = tempnam('/tmp', 'gz_fix');
file_put_contents($f, "\x1f\x8b\x08\x00\x00\x00\x00\x00" . $data);
return file_get_contents('compress.zlib://' . $f);
}
?>
gabriel at bumpt dot n-et ¶
5 years ago
To uncompress in PHP a string that has been compressed using MySQL's COMPRESS() function, you need to discard the first four bytes of the binary data:
<?php
/*
* Example:
*
* insert into mytable (myfield, ...) values (COMPRESS('foobar'), ...)
*
* then:
*/
$compressed = //...select myfield from mytable where...
/*
* then:
*/
$uncompressed = gzuncompress(substr($compressed, 4));
?>
Of course, you can use MySQL's UNCOMPRESS() function.
I was just providing an alternate method.
emanuele at fondani dot it ¶
6 years ago
Note that the manual states that the input parameter must be a string compressed with gzcompress(), so it is not guaranteed that it will compress ANY zlib compressed string.
I realized this while decompressing some compressed string in a pdf file. The gzuncompress() function produces a data error, but the string can be successfully decompressed with other zlib decompressors.
More info here:
http://bugs.php.net/?id=39616
chappy at citromail dot hu ¶
7 years ago
Reading an ID3v2.3+ tag it is versy useful, because these tag's frames might be compressed. Zlib compressed frame layout (ID3v2.3):
Descriptior Size
-------------------
Frameheader:
Frame id: 4 bytes
Frame size (full frame size - frameheader size): 4 bytes
Frame flags: 2 bytes
The 2nd byte's 7th bit must be 1 (e.g.: %1xy00000)
Frame content decrompessed size: 4 bytes
--------------------
Framecontent:
Compressed string described in 'frame size'
<?php
$frame="[read from a mp3 file]";
$frame_id=substr($frame,0,4);
/*....*/
$cs=substr($frame,10,4);
$checksize=$cs[3]*16777216+$cs[2]*65536+$cs[1]*256+$cs[0];
$content=substr($frame,14,$contentsize);
$content=gzuncompress($content);
if(strlen($content)!=$checksize){
echo 'Error whil uncrompessing frame data<br>';
}
echo $content;
?>
PapaPingouin ¶
7 months ago
gzuncompress make un error if the string is not a gzcompress string.
You can test the header string before gzuncompress
FR : gzumcompress génère une erreur si la chaine n'est pas au bon format.
Vous pouvez tester le header de la chaine avant d'appeller gzuncompress
header :
0x78 0x01 (level 1)
0x78 0x5e (level 2,3,4,5)
0x78 0x9c (level 6)
0x78 0xda (level 7,8,9)
<?php
if( ord($string[0]) == 0x78 && in_array(ord($string[1]),array(0x01,0x5e,0x9c,0xda)) )
$uncompressedstring = gzuncompress( $string );
?>